The present invention relates to a straightening machine in which a plurality of frames or stands are mounted on an elongated machine bed displaceable with respect to each other in direction of the movement of the workpieces, and in which each of the stands carries a cage provided with a set of four straightening rolls in which the rolls are mounted for rotation about axes extending normal to the axis of the workpiece.
For straightening workpieces at high speed, in the order of about 1000 meters per minute, only so-called roll straightening machines are usable, since in other known straightening machines, in which either the workpiece rotates or the straightening tools are orbited in a circular path about the workpiece axis, the thereby occurring centrifugal, respectively inertia forces become unacceptably large at the aforementioned speed of travel of the workpieces to be straightened. The known roll straightening machines with two, respectively two times two rows of rolls have, however, the disadvantage that during bending in a second plane the straightening result produced in the preceding plane will be detrimentally affected.
The German Offenbarungsschrift No. 2,126,371, discloses a method in which the workpieces to be straightened are successively bent in directions normal to each other. In this method the workpieces are however bent about their main axes of inertia. This will result in extremely high maximum bending forces. The straightening frames through which the workpieces have to twist are telescopically moved apart. A construction for carrying out the method disclosed in the aforementioned German Auslegesschrift is, however, not disclosed therein. The adjustment of the individual radial displacements of the straightening roll sets in their frames is, during carrying out the disclosed method, extremely difficult. A great number of individual adjustments on the respective straightening frames is necessary whereby the radial adjustments of the individual straightening roll sets and the axial movement of the frames have to be carefully harmonized with each other. Thereby the action of the individual adjustment on one frame is not foreseeable.
The U.S. Pat. No. 2,411,395 discloses a straightening machine for tubes in which three straightening frames are provided. The three frames form together a bending triangle. Each frame carries four rolls constructed and arranged to substantially enclose the tube to be bent. The tube to be bent carries out a spiral movement during the straightening operation. For this reason, the straightening machine disclosed in the U.S. patent is not suitable for a straightening speed of the above-mentioned magnitude. The U.S. discloses already that the straightening frames are preferably adjustable with respect to each other in direction of the movement of the workpiece by means of a double spindle arrangement provided in the machine bed. In this machine there exists also a great number of adjusting possibilities for each straightening frame. The machine disclosed in the aforementioned patent differs however essentially from the machine of the present invention in that the disclosed machine is only suitable for straightening material of circular cross-section.